JP5467041B2 - Cellulose fiber degumming method - Google Patents

Description

  The present invention relates to a method for degumming lignocellulosic fibers, in particular, a method for producing dissolving pulp fibers.

Pulp is a collective term for a wide range of technically different products obtained from complex manufacturing processes involving the chemical and / or mechanical treatment of various types of plant material. Currently, about 90% of global pulp production is based on wood, with the remaining 10% starting from straw, bamboo, bagasse, kenaf, flax, hemp, cotton, etc. Pulp is mainly used as a main component in the manufacture of paper and cardboard. Smaller amounts of pulp are in a variety of products-rayon, photographic film, cellophane, and gunpowder.
The highest grade pulp is chemical grade or dissolution grade pulp. Dissolving pulp is a value-added product, for example:
・ Viscose fiber (rayon) or film, because pulp is dissolved in alkaline carbon disulfide (xanthogenation), it is produced by forming xanthate as an intermediate product and passing this solution through an orifice to an acid bath What will be done.
Cellulose derivatives such as cellulose acetate, ethyl cellulose, cellulose nitrate (nitrocellulose, cotton powder), carboxymethyl cellulose (CMC)
Used in the manufacture of

The production of dissolving pulp usually uses kraft or sulfite pulping of wood (both softwood and hardwood) or soda pulping of cotton linter. When pulping wood for dissolving pulp, the yield bleached to obtain a purer pulp is only 32-36%. Cellulose content is generally 88-93% (in the case of commercial grade viscose), but may be as high as 98% for more severe end use (eg: tire cords). The content of extracted components, lignin, iron and ash is also low. Viscosity (ie: DP) is another important property and the actual level depends on the end use of the pulp. For commercial grade viscose, the viscosity may be from about 350 to about 550 ml / g. High grade dissolving pulp may exceed 700 ml / g.
In order to produce dissolved pulp, conventional kraft pulping is modified to include a pre-hydrolysis stage in which hemicellulose is hydrolyzed and removed prior to main cooking. For this prehydrolysis step, a dilute acid or dilute alkali is used, or direct steam is used. This additional stage almost doubles the total cooking time relative to normal kraft cooking. The cold alkaline extraction stage of the bleaching sequence further removes non-cellulose components.
Acid sulfite pulping is performed at high temperature and low pH to achieve the desired hemicellulose degradation. Bleaching includes a high temperature alkaline extraction stage that further removes non-cellulose components.
Some studies have shown that dissolving pulp can be obtained from bleached hardwood kraft market pulp or high quality wood pulp rich in hardwood fiber. The sequence included two cold alkali extraction steps with xylanase treatment in between. [Jackson, LS et al. Production of dissolving pulp from recovered paper using enzymes. TAPPI Journal, March 1998].

Prior art methods of producing these dissolving pulps use large amounts of chemicals and energy and require complex black liquor recycling processes. A separate bleaching step is required after alkaline degumming.
Therefore, there is a need for a process for producing degummed pulp suitable for producing dissolved pulp that improves the disadvantages of the prior art.

In one aspect, the present invention is a method for degumming cellulose fibers, wherein the fibers are about 5% to about 30% (v: v) aqueous ammonia and about 0.5% to 3% (relative to OD fibers). And a degumming solution containing hydrogen peroxide at a temperature of about 50 ° C. to about 200 ° C. and a liquid and solid content consistency (v / w) of about 3: 1 to about 20: 1. Including the method. The degumming solution may further contain 0% to 10% (based on OD fibers) potassium hydroxide and 0% to 0.2% (based on OD fibers) anthraquinone.
In one embodiment, the cellulose fibers are hardwood, coniferous, and bast fiber plants such as hemp, flax, kenaf, flaxseed, jute, ramie, other dicotyledonous plants with fibrous phloem such as cereals, perennials, etc. It may contain grass or legumes.
In one embodiment, the degumming liquid is recovered after degumming, the aqueous portion is recycled to supply ammonia, and the solid portion is recovered in a waste recovery stream. In one embodiment, the solid portion is recovered and processed to form a fertilizer.
The degummed fibers will be bleached to form dissolving pulp.

In another aspect, the present invention is a method of forming dissolving pulp from a bast fiber plant:
(a) a step of pulping a plant fiber with a degumming solution containing ammonia and hydrogen peroxide;
(b) recovering and recycling the aqueous portion from step (a);
(c) collecting the pulped fiber and bleaching to obtain a dissolving pulp.
Bast fiber plant fibers may include hemp, flax, kenaf, flaxseed, jute, or ramie fibers.
In the figure, similar elements are assigned similar symbols. The drawings are not necessarily to scale, emphasis instead being placed on the principles of the invention. Furthermore, each of the illustrated embodiments is only one of many possible arrangements that use the basic concepts of the present invention. Briefly describe the drawings as follows:

FIG. 1 is a schematic diagram of one embodiment of the present invention.

  The present invention relates to a method for degumming cellulose fibers, in particular a method for producing high quality dissolving pulp. In describing the present invention, all terms not defined herein have a common meaning recognized in the art. As long as the following description is an individual embodiment or specific use of the present invention, this is merely an example, and does not limit the invention described in the claims. The following description is intended to cover all changes, modifications, and equivalents included in the spirit and scope of the invention as defined in the appended claims.

In general, the present invention includes a method of degumming cellulose fibers using ammonia. The degummed fibers are then bleached using processes well known in the art, such as chlorine bleaching, elemental chlorine-free (“ECF”) bleaching, or chlorine-free (“TCF”) bleaching. May be. Given the environmental benefits of ECF and TCF bleaching, preferred embodiments use these techniques.
In one embodiment, the degumming process comprises cellulosic fibers such as hardwood, conifers, bast fiber plants such as hemp, flax, kenaf, flaxseed, jute, ramie, other dicotyledonous plants with fibrous phloem, For example, it is used for cereals, perennial grasses, or legumes. In one embodiment, the cellulose fibers comprise hemp or flax fibers.
Methods for separating bast fibers from plant stems are well known in the art and do not require further description herein. One exemplary method of peeling bast fiber plants is described in Applicant's co-pending US patent application filed May 23, 2008, entitled “Decortication Process”.
In the present invention, the inventors have surprisingly found that high quality melt grade pulp can still be obtained with the milder conditions found in the prior art.

In one embodiment, the separated bast fibers are mixed with ammonia at an elevated temperature in the reactor (10). In one embodiment, ammonium hydroxide is used at a concentration of about 5% to 30% by volume and a temperature of about 50 ° C to about 200 ° C. Preferably, the temperature is from about 90 ° C to about 150 ° C, such as 90 ° C, 100 ° C, 120 ° C, or 150 ° C. In one embodiment, an amount of chlorine-free bleach, such as hydrogen peroxide, is used that simultaneously bleaches the fiber. This ammonia peroxide degumming process may be performed at a liquid: solids ratio (v: w) concentration of about 3: 1 to about 20: 1 for about 1 to 6 hours. One skilled in the art can determine the appropriate conditions by varying these parameters without undue experimentation. As is well known, an increase in the degree of one parameter will allow a decrease in the other. For example, the use of higher temperatures or higher concentrations of ammonia can allow for shorter cooking times. Alternatively, low concentrations of ammonia will require higher temperatures or longer cooking times to achieve similar results.
The amount of hydrogen peroxide is less than 3% (by weight of oven dried (OD) fiber), preferably less than about 2%, and most preferably less than about 1%.
In one embodiment, an alkali such as potassium hydroxide (KOH), potassium carbonate, or magnesium hydroxide may be added to the degumming solution at a concentration of 0% to about 10% (based on OD fibers). . The degumming solution may further contain 0% to 0.2% (based on OD fibers) of anthraquinone. Both alkali and anthraquinone aid in delignification of cellulose fibers and may therefore be preferred for treating more lignined materials such as wood fibers and grain straws.
After pulping and degumming in the reactor, in one embodiment, the liquid is recovered and sent to the evaporator (20), where ammonia is recovered in the ammonia recycling tank (30) and the ammonia in the reactor (10). Used as a source. An ammonia supply source (40) is supplied. The solid content remaining from the evaporator (20) contains lignin and hemicellulose together with a small amount of ammonia, is taken out to a solid content recovery tank (50), and can be processed into a fertilizer in a waste recovery stream (60).
The pulped and degummed fibers are then washed in a wash tank (70), in one embodiment to a neutral pH, and the resulting fibers are then sent to bleach (80). The washing water contains ammonia and peroxide, and may then be recycled to the ammonia recycling tank (30).
In one embodiment, in the dissolving pulp process, the degummed fiber is then bleached in a TCF or ECF bleaching process. For example, the fibers may be bleached in a three or four stage ECF process that is followed by cold alkaline extraction. Exemplary conditions are shown in Table 1 below:

^* 冷アルカリ抽出段階におけるNaOH濃度は、10% w/wであった。
“D”は、二酸化塩素の使用を意味する。
“E_p”は、過酸化水素によるアルカリ抽出を意味する。
“E”は、アルカリ抽出を意味する。 table 1

^* NaOH concentration in the cold alkali extraction stage was 10% w / w.
“D” means the use of chlorine dioxide.
“E _p ” means alkaline extraction with hydrogen peroxide.
“E” means alkaline extraction.

In one embodiment, the ECF process is preferred because chlorine dioxide is believed to dissolve non-bast fibers in the bast fiber feedstock.
The resulting dissolving pulp is of high quality. Dissolving pulp from bast fiber plants such as hemp can yield yields in excess of 55%, whiteness greater than about 92% ISO, alpha-cellulose content greater than 98% and viscosity greater than 650 ml / g Can be achieved by the method of the present invention.

  In the examples shown below, “AP pulping” means ammonia peroxide pulping, the abbreviation “L: S” means the ratio of liquid to solids, and the abbreviation “AQ” means anthraquinone. Means content.

Example 1
AP pulping of hemp bast fibers at cooking temperature of 150 ℃ Table 1-1. AP pulping conditions

^* 冷アルカリ抽出段階におけるNaOH濃度は、10% w/wであった。 Table 1-2. ECF bleaching conditions

^* NaOH concentration in the cold alkali extraction stage was 10% w / w.

Table 1-3. Properties of hemp bast fiber dissolving pulp

Example 2
AP pulping of hemp bast fibers at 90 ° C cooking temperature Table 2-1. AP pulping conditions

^* 冷アルカリ抽出段階におけるNaOH濃度は、10% w/wであった。 Table 2-2. ECF bleaching conditions

^* NaOH concentration in the cold alkali extraction stage was 10% w / w.

Table 2-3. Properties of hemp bast fiber dissolving pulp

Several references or patents are included in this application to more fully describe the state of the art to which this invention pertains. Where possible, the disclosure of each of these references is hereby incorporated by reference as if fully set forth herein.
The term “including” is used herein in a non-limiting sense and means “including without limitation or excluding other variations”.

Claims (14)

A method for producing dissolving pulp from cellulose fibers, the fibers comprising 5 % to 30 % (v: v) aqueous ammonia and 0.5% to 3% (relative to OD fibers) hydrogen peroxide. in degumming solution containing bets, at a temperature of 5 0 ℃ ~2 00 ℃, 3 : 1 ~2 0: 1 liquid and solid concentration (v / w) comprising the step of degumming said method.   The method according to claim 1, wherein the degumming solution further comprises potassium hydroxide.   The method according to claim 1 or 2, wherein the degumming solution further contains anthraquinone.   The method of claim 1, wherein after degumming, the degumming fluid is collected and processed to separate the ammonia stream for reuse in the process and the solid fraction.   5. The method of claim 4, wherein the solid portion is collected and processed to form a fertilizer.   The method of claim 1, further comprising bleaching the degummed fibers to form a dissolving pulp.   2. The method of claim 1, wherein the cellulose fibers comprise bast fiber plant fibers.   8. The method of claim 7, wherein the bast fiber plant is one of hemp, flax, kenaf, flaxseed, jute or ramie.   9. The method of claim 8, wherein the bast fiber plant is hemp.   9. The method according to claim 8, wherein the bast fiber plant is flax.   9. The method according to claim 8, wherein the bast fiber plant is kenaf.   The method of claim 1, wherein the cellulose fiber comprises wood fiber, grain straw fiber, perennial grass fiber, or legume fiber.   7. The method according to claim 6, wherein the bleaching step comprises an ECF bleaching step or a TCF bleaching step. The method of claim 1, wherein the aqueous portion is recovered from the degumming step and recycled .

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